1. Field of the Invention
The present invention relates to a method and apparatus for large-area electrical contacting of semiconductors, and more specifically to the contacting of the semiconductor crystal body with the assistance of electrolytes, whereby a first cell having a first electrode is applied to a front side of the semiconductor body, a second cell having a second electrode is applied to the rear side of the semiconductor body, at least the second cell is filled with an electrolyte that contacts the electrode with the rear side of a semiconductor crystal body, and a voltage is applied between the two electrodes, with which method and apparatus good electrical contacts with high-current loadability can be produced.
2. Description of the Prior Art
The production of such contacts to semiconductor surfaces is of technical interest for many reasons. One is, for example, for use in electro-chemical processes wherein portions of the surface of the semiconductor are exposed to an electrolyte. Some applications with reference to the example of silicon are: electro-polishing, hole etching, production of what are referred to as porous silicon layers, electrode deposition, and mensurational purposes.
In the aforementioned processes, the rear side or, more generally, portions of the surface not exposed to the electrolyte were previously provided with an ohmic contact for supplying the required current. Producing good electrical contacts on semiconductors, however, is generally a difficult and non-destruction-free process that usually requires a pre-treatment of the semiconductor and the application of one or more metal layers. Relatively good contacts can also be produced by rubbing indium-gallium eutectic into the rear side to be contacted, as described in the article by Lehmann et al in the JPL Publication, Vol. 84, No. 23, 1983, pp. 527 et seq., The method, however, is not suitable for large-area contacts and for industrial-scale applications.
The manufacture of less good (non-ohmic) contacts by pressing metal plates or tips on is, in fact, more simple, but often does not satisfy the requirements that are made of the contact resistance and the uniformity of the current flow through the wafer.
U.S. Pat. No. 4,628,591, Zorinsky et al, discloses a power supply via an electrolyte contact. The rear surface is thereby, likewise, brought into contact with an electrolyte. An electrolyte is located therein that is connected via a DC voltage source to the electrode in the electrolyte at the front surface of the semiconductor wafer (working side). The required current flow through the electrolyte at the front side causes a polarization of the DC source such that a current can flow through the electrolyte at the rear side, only given extremely high voltages, since the electrolyte cell, at the rear side, represents a diode polarized in the non-conducting direction. The magnitude of the required voltage is dependent on the specific resistance .rho. of the semiconductor crystal, so that the method can only be utilized for semiconductors having a specific resistance .rho. approximately equal to or less than 0.1 ohm cm.